Three firefighters have died after their vehicle crashed and was caught by flames as they battled a blaze in Washington state, authorities said.

Four other firefighters were injured as crews on several fronts fought against raging wildfires advancing on towns in the north-central part of the state.

The fatal crash occurred near the town of Twisp, the National Forest Service said.

"The firefighters were engaged in initial attack operations and were involved in a vehicle accident when it is believed that the fire overtook the vehicle," said the statement from Okanogan-Wenatchee National Forest, relaying information from Okanogan County Sheriff Frank Rogers.

"It was a hellstorm up here," Mr Rogers told KXLY-TV of Spokane. "The fire was racing and the winds were blowing in every direction and then it would shift. It was tough on them up here."

The White House said president Barack Obama had been informed of the deaths. He directed the administration to stay in touch with state and local officials and to provide federal assistance as necessary.

Governor of Washington Jay Inslee requested a federal emergency declaration to provide more help to pay for fighting the wildfires in the state.

The deaths came after officials urged people in the popular outdoor recreation centres north east of Seattle to evacuate as a fire near Twisp grew to about two square miles.

A larger group of fires burning to the east covered about 50 square miles and prompted the evacuation of Conconully, home to about 200 people.

To the south, more than 1,100 firefighters were battling a fire that topped 108 square miles and was threatening the resort town of Chelan.

Drought and heat have combined to make this fire season one of the most active in the US in recent years.

Nearly 29,000 firefighters are battling 100 large blazes across the West, including in Idaho, Oregon, Montana, Washington and California.